Easiest way to count occurrences of DMatch in a vector<DMatch>

asked 2017-11-21 07:18:03 -0600

Grillteller gravatar image


I have a vector of matches (vector<DMatch>) in which are multiple same matches. Now I want to get the best (so the match with the most occurences) out of this vector.

For understanding: I calculate a Fundamental matrix a lot of times for the same image pair but the calculation is everytime slightly different. I always save the best matches (most of the times: 7 per iteration) in my vector<DMatch>. Here is the code snippet:

    vector<DMatch> all_inlier_matches;

    // This part is in a for loop with several iterations
    vector<DMatch> good_matches, good_matches_2, sym_matches;
    BFMatcher matcher;
    vector<DMatch> matches, matches_2;
    float ratio_Lowe, ratio_Lowe_2;

    BruteForceMatching(descriptors_1, descriptors_2, good_matches, matches, ratio_Lowe);
    BruteForceMatching(descriptors_2, descriptors_1, good_matches_2, matches_2, ratio_Lowe_2);

    symmetryTest(matches, matches_2, sym_matches); // Calculation of the best matches

    for (size_t i = 0; i < sym_matches.size(); i++) {
       all_inlier_matches.push_back(sym_matches[i]);  // Push_back ~seven matches per iteration;

Now I want the best of my best matches, so the matches which occur for example more than 5 times. So what is the structure of a DMatch, how can I compare them to each other and how can I count same occurences? I read something about counting in a vector with unordered map but I can hardly understand it.

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please have a look at the DMatch class

what would you consider "same" here ? like same indices, but distance differs ? are matches with swapped indices "same" ?

berak gravatar imageberak ( 2017-11-23 03:22:14 -0600 )edit

You are right. I saw now that you can't really compare the matches itself so I extracted the coordinates of the matched points in two vector<Point2f>. Now I can just compare my left image point coordinates with my right image point coordinates. When I have equal coordinates on different positions in the vector for both images I have the same match.

Grillteller gravatar imageGrillteller ( 2017-11-23 05:36:50 -0600 )edit